1. Field of the Invention
The invention relates to fuel injectors for internal combustion engines and, in particular, to a fuel injector having a stator nut used as an accumulator.
2. Background Art
It is known practice to use fuel injectors for internal combustion engines, particularly for each cylinder of multi-cylinder engines. The injector includes an injector needle valve assembly that receives pressurized fluid from a fuel injector pump. The pump in turn is driven by the engine camshaft. Fuel injection pulses are delivered to the combustion camber of the internal combustion engine. The camshaft, which is driven at one-half engine speed, develops a pressure pulse during the injection phase of the four-stroke engine cycle.
A fuel injection plunger is driven by a cam surface on the engine camshaft. The plunger and its associated fuel cylinder define a fuel pumping chamber. The fuel supply for a control valve assembly is a low pressure fuel pump that circulates fluid through the control valve at intervals in the engine cycle when the control valve is in an open position. A low pressure fuel passageway directs fuel from the control valve to the fuel pumping chamber. When the valve is in a closed position, direct fluid communication between the fuel pump and the fuel pressure chamber is interrupted as the plunger is stroked during a fuel injection event. The stroked plunger creates a high injection pressure in a nozzle fuel supply passageway. The timing of the opening and the closure of the control valve is controlled by a solenoid actuator under the control of an electronic engine control system.
The fuel pressure chamber communicates with an injection nozzle orifice valve that registers with an injection orifice. Pressure developed in the fuel pressure chamber acts on a differential area on the needle valve to shift the needle valve to an open position during the injection event. Movement of the needle valve under pressure is opposed by a needle valve spring that normally tends to keep the needle valve closed.
The needle valve spring is situated in a spring cage, which forms a part of the fuel injection assembly. The needle valve has a stem that defines a guide surface.
The present invention discloses an electromechanical fuel injector for an internal combustion engine. The fuel injector includes a pump unit and a control valve assembly in communication with the pump unit. The control valve assembly includes a body and a stator. The fuel injector also includes a stator nut cooperable with the valve body to secure the stator to the valve body, and at least one expansion tank to accumulate pressure created by the pump unit. The fuel injector may also include a spacer positioned between the stator and the valve body to create a passageway to expansion tanks located between the stator and stator nut.
The down stroke of the plunger creates high injection pressure in the fuel passageway. When the valve element opens to end the injection of fuel, the built up pressure is communicated to the stator and the armature cavity. In known injectors, this may cause fuel to leaks, which can cause failure of the stator and related actuator components.
The present invention avoids this problem by providing expansion tanks that accumulate pressure created by the down stroke of the plunger. This reduces the armature cavity pressure, thereby extending the useful life of the fuel injector.
The above features of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.